NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 17, 5:24 AM PST, 7 hours 36 minutes earlier.
Area forecast discussion, Nov 17, 5:24 AM PST, 7 hours 36 minutes before
Area Forecast Discussion
National Weather Service Medford OR
524 AM PST Sun Nov 17 2024
.DISCUSSION...A series of systems will lead to a complex and
unsettled week of weather across southern Oregon and northern
California. After this morning's warm front and this afternoon
into tonight's cold front passes through, an atmospheric river
will move into the area Tuesday through at least Wednesday, and
could stall with a longer duration of strong winds and heavy
precipitation during the second half of the week.
Updates this morning include: a High Surf Advisory for southern
Oregon beaches this evening through Monday afternoon, a Wind
Advisory from now into this evening for much of Lake County and
the Warner Mountains of eastern Modoc County, an adjustment to
begin the southern Oregon Cascades and Siskiyou Mountains portion
of the Winter Storm Warning a few hours earlier (at 1 PM this
afternoon) with the hazard continuing through Monday evening.
Also, more detail added to the Flood Potential Outlook with
moderate to heavy rain focused from the coast to Interstate 5
during Tuesday night at least into Wednesday night. Lastly, a High
Wind Watch has been issued for the coast, Shasta Valley, and much
of the east side Tuesday afternoon into Wednesday morning.
Key Points:
*Gusty southwest winds increasing this morning into this evening,
strongest for the coast, higher terrain, and east side.
*Snow levels quite high this morning will quickly crash late this
afternoon through tonight into Monday as a winter storm brings
traditional wind and snow impacts to the area, with a focus on
the Oregon Cascades.
*An atmospheric river will then approach the area on Tuesday and
could stall providing hydrologic concerns with significant rises
for creeks and rivers near the coast and the coast range with
heavy rainfall, and moderate mountain snows.
*The front bringing the strong atmospheric river is also likely
to bring strong winds to the coast, Shasta Valley, Rogue Valley,
and the East Side Tuesday afternon at least into Wednesday
morning.
*Given model differences, the one aspect of the Tuesday/Wednesday
storm that we have not strongly advertised just yet is the
potential for heavy snow. The timing and track of the front will
have a big effect on amounts and snow levels. We will look to
determine the appropriateness of Winter Storm Watches for the
next forecast issuance this afternoon. For now, snow levels look
to most likely be around 3500 to 4500 feet during Tuesday night
and Wednesday with heavy snow for Siskiyou County, the Cascades
and Siskiyou Mountains, and northern Klamath County. This will be
a heavy, wet snow which could enhance hazardous conditions.
*Uncertainty/model variability increases after Wednesday. It is
the second half of the week that is likely to be a difference
maker in the extent of impacts, especially regarding coastal
river rises. The next wave on the stalled front may be focused
south and southwest of our area, along the northern California
coast. But, there is also a sizeable, nearly as large, contingent
of ensemble solutions (including the operational GFS) that bring
another wallop focused upon Curry, Josephine, and Siskiyou
counties Wednesday night through Thursday night.
*Our weather pattern looks to remain active at the end of the
week, Friday into Saturday with another frontal system that only
looks weak in comparison.
&&
.AVIATION...17/12Z TAFS...A cold front will move across
the area today. Rain across NW sections early this morning will
overspread the remainder of the area later this morning and this
afternoon. Widespread low conditions exist area wide this morning
ranging from MVFR to LIFR with higher terrain obscured. These
conditions will persist for much of the day, only temporarily rising
to VFR at times here and there. Stronger winds aloft will lead to
some turbulence as well, especially near mountain ranges. Gusty
winds will develop east of the Cascades this afternoon/evening with
gusts to around 30kt at Klamath Falls, but perhaps even a bit higher
than that farther east from Winter Rim south to the Warner Mtns and
eastward. Colder air arriving aloft could bring thunderstorms to the
coastal waters this afternoon/evening, and for some areas just
inland, mainly west of I-5 near Roseburg and Highway 199 west of
Grants Pass/Cave Junction. Freezing levels will drop quickly behind
the front to mountain passes by this evening, then as low as 2500
feet overnight into Monday morning. This will result in widespread
MVFR/IFR conditions with mountain obscurations continuing. -Spilde
&&
.MARINE...Updated 230 AM PST Sunday, November 17, 2024...
Steep to very steep seas are expected today as another westerly
swell builds into the coastal waters. Seas peak in the 15-20 foot
range with dominant wave period of 13 seconds. We've upgraded to
Hazardous Seas Warning for most areas, except the far SE sections
(mainly PZZ356, but also a portion of SE PZZ376) where conditions
are primarily small craft advisory. Southwest winds become west or
even possibly northwest this afternoon/evening with peak winds of 20-
30 kt and gusts of 35 kt. There is also a chance of thunderstorms.
Brief gusts in excess of 35 kt are possible in some of the stronger
cells along with lightning. These conditions persist through Monday
afternoon, then seas subside briefly Monday night.
Tuesday into Wednesday, surface low pressure in the NE Pacific will
deepen rapidly as it heads NE just outside 130W. This system will
"bomb out" (a pressure drop of 24 mb or more in 24 hours) with a
large portion of members indicating the pressure dropping below 950
mb as it reaches 46N and 132W by Tuesday evening. These solutions
have been consistent over the last couple of days. This will send a
very strong cold front and associated atmospheric river toward the
coast, impacting the marine waters with storm force winds (40-50kt
with gusts of 65 kt) and dangerous seas in the 19-24 foot range.
Some of the highest members of the guidance show peak wave heights
exceeding 25 feet at Buoy 15 with a rapid increase in wind waves.
That gives you an idea of the potential of this storm. Given the
consistency in the guidance, we have issued a Storm Watch for all
waters from 18z Tuesday through 18Z Wednesday. Mariners should
expect dangerous wind and sea conditions to persist through at least
mid week with hazardous conditions possible through Friday. Keep
checking back here for updates. -Spilde
&&
.BEACH HAZARDS...Updated 230 AM PST Sunday, November 17, 2024...
Large, west swell will build into the waters tonight through Monday
afternoon. We have issued a high surf advisory during this time with
breaking waves of 20 to 23 feet, bringing dangerous conditions to
coastal areas/beaches. Seas lower slightly Monday night but a
stronger frontal system will move through Tuesday into Wednesday
bringing building seas with high surf conditions likely again.
Models support advisory conditions at a minimum, but with storm
force south winds expected, this could result in warning level
conditions, especially at south-facing beaches and ports. Please
exercise extreme caution if you are planning to head to the beaches
or even just take a trip to the coast through midweek. Be aware that
conditions will be very hazardous with dangerous surf conditions
much of the time. -Spilde
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Monday for ORZ025-027-028-030.
High Wind Watch from Tuesday afternoon through Wednesday morning
for ORZ021-022-024-030-031.
Wind Advisory until 7 PM PST this evening for ORZ030-031.
High Surf Advisory from 7 PM this evening to 4 PM PST Monday for
ORZ021-022.
CA...Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Monday for CAZ080-083-085.
High Wind Watch from Tuesday afternoon through Wednesday morning
for CAZ081-085.
Wind Advisory until 7 PM PST this evening for CAZ085.
PACIFIC COASTAL WATERS...High Surf Advisory from 7 PM this evening to
4 PM PST Monday for PZZ350-356.
Small Craft Advisory until 10 AM PST Tuesday for PZZ356-376.
Storm Watch from Tuesday morning through Wednesday morning for
PZZ350-356-370-376.
Hazardous Seas Warning until 4 PM PST Monday for PZZ350-370-376.
Small Craft Advisory from 4 PM Monday to 10 AM PST Tuesday for
PZZ350-370.
&&